An active pixel sensor (APS) converts an optical signal into an electrical signal. The active pixel sensor may include a charge coupled device (CCD) type APS and a complementary metal oxide semiconductor (CMOS) type APS. The CMOS type APS can be fabricated on a silicon substrate by a semiconductor manufacturing process, so that the CMOS type APS can be easily integrated into a peripheral system having an amplification circuit and a signal processing circuit.